The invention relates to a process for producing a concentrate of denatured whey protein aggregates, preferably having a mean aggregate size (median) in the range from 1 to 4 xcexcm, and to a stable foam product obtainable by this process.
Proteins in foods frequently do not exist as soluble individual molecules, but in the form of relatively large aggregates or particles. Such particulate structures can exist naturally, as is the case with casein micelles in milk or may not be formed until during the production process, for instance in the production of ricotta by coagulating the whey proteins [KALAB, M. (1990) xe2x80x9cMicroparticulate protein in foodsxe2x80x9d, Journal of the American College of Nutrition, 9, 374-387]. The mouthfeel caused by such aggregates or particles is essentially influenced by their size. Particles which are smaller than 0.1 xcexcm are not perceived, so that a watery-empty impression results [Lxc3x9cTH, A. (1991): Frettreduktion mit Hilfe mikropartikulierter Proteinexe2x80x94ein neues Konzept zur Entwicklung von xe2x80x9cLight-Produktenxe2x80x9d [Fat reduction using microparticulate proteinsxe2x80x94a novel concept for developing xe2x80x9clight productsxe2x80x9d , DMZ-Lebensmittelindustrie und Milchwirtschaft, 112, 762-766].
Protein aggregates which are in the size range of emulsified fat droplets, that is to say between 0.1 and 10 xcexcm, can cause a creamy-smooth mouthfeel [MILLER, M. S. (1994) xe2x80x9cProteins as fat substitutesxe2x80x9d In: Protein Functionality in Food Systems (Editors: HETTIARACHCHY, N. S.; ZIEGLER, G. R.), New York, Basle, Hong Kong].
Larger particles are detected in the mouth individually and are perceived as floury to sandy. However, it is not possible to define an exact limit of particle size at which roughness occurs, since subjective factors also play a role. Cited data extend from 3 to 40 xcexcm. Other properties of the particles, such as shape, deformability and surface structure, also play a role, as do the properties of the surrounding environment, in particular its viscosity (MILLER, op. cit.).
FR-A 1 453 815 discloses a process for recovering the proteins remaining in the whey after coagulating milk, in which the whey is first adjusted to a pH between 4.6 and 7.0, in the case of the example to a pH of 4.65, and is then heated to a temperature between 70xc2x0 C. and 100xc2x0 C. in the case of the example 90xc2x0 C., in order to precipitate out the proteins. The precipitated proteins are then removed by a centrifugation. Generally no information is provided on the size of the resultant protein aggregates in this publication. At the pH of 4.65 used in the case of the example, the proportion of protein aggregates in the desired order of size to achieve a creamy-smooth mouthfeel is low, however, and the yield of the process is therefore poor in this respect.
VISSER and BAKKER (EP-A 0 347 237) describe a process in which whey proteins are heated at low starting concentrations at temperatures below 100xc2x0 C., in particular between 65xc2x0 C. and 75xc2x0 C. Within this temperature range the heating time is set so that no more than 10% of the proteins are denatured, that is to say become insoluble at a pH of 4.6. The denatured proteins are then concentrated, so as to give a dispersion of non-aggregated macrocolloidal particles having diameters of 0.1 to 10 xcexcm.
Under similar heating conditions (60xc2x0 C. to 80xc2x0 C.), according to HAKAART et al. (EP-A 0 412 590) a food composition having an elevated content of xcex1-lactalbumin can be produced from whey having a protein content of less than 8% or from an xcex1-lactalbumin-enriched fraction, with simultaneous application of a low amount of shear. The non-aggregated microcolloidal particles which are obtained in this process have a mean particle size in the range from 0.1 to 10 xcexcm.
WO-A 92/20239 [ASHER et al.] describes a process for producing a fat substitute for use in ice cream manufacture, in which, via ultrafiltering whey, a whey concentrate (WPC) is obtained and by subsequent short-time heating of the resultant whey concentrate to between 75xc2x0 C. and 85xc2x0 C., the whey proteins are partially denatured. This treatment leads to a product of coagulated particles of a size which is not defined in more detail. If the denaturation conditions are intensified in order to obtain a higher degree of denaturation, in the case of this known process a product is obtained having larger particles which can readily be differentiated, which makes it completely unsuitable for use in ice cream manufacture.
A subsequent mechanical treatment of heat-denatured whey proteins, in particular high shear, can also lead to aggregate sizes in the micrometer range: in a process developed by PAQUIN et al., [PAQUIN, P.; LEBEUF, Y.; RICHARD, J. P.; KALAB, M. xe2x80x9cMicroparticulation of milk proteins by high pressure homogenization to produce a fat substitutexe2x80x9d in: IDF Special Issue 9303: Protein and Fat Globule Modifications 389-396 (1993], ultrafiltered and diafiltered whey is first heated in the neutral or acidic pH range at 95xc2x0 C. for 5 min. This gives a roughly 90% denaturation and aggregation of the whey proteins. The heated concentrate is then homogenized in a special high-pressure homogenizer, called a microfluidizer, at a pressure of 750 bar. The coarsely aggregated structure is broken down by this treatment into small spherical particles of about 1 to 10 xcexcm in diameter.
Comparable particle sizes were found by SPIEGEL, T. KESSLER, H. G. [xe2x80x9cContinuous formation of gel structures and stable foams based on a heat treated and acidulated whey protein concentratexe2x80x9d in Texture of Fermented Milk Products and Dairy Desserts, Proceedings of the IDF Symposium in Vicenza, 106-114, (1998)], when a whey concentrate containing 10% protein and 13% lactose was heated at 80xc2x0 C. and, during the subsequent cooling, was subjected to intensive shear treatment in a scraped-surface heat exchanger.
These known processes share the fact that the yield of protein aggregates in the desired size of about 0.1 to 10 xcexcm is low. Furthermore, these processes are for the most part complicated and expensive and therefore not of interest for industrial application.
The object of the invention is therefore to provide a process for producing denatured whey protein aggregates, preferably having a size of essentially 0.1 xcexcm to 10 xcexcm [mean aggregate size (median) in the range from 1 to 4 xcexcm] which is simple to carry out and is able to provide the desired protein aggregates reliably and in high yield.
This object is achieved by a process for producing a concentrate of denatured whey protein aggregates, preferably having a mean aggregate size (median) in the range from 1 to 4 xcexcm, which comprises the steps that
a) an aqueous solution containing whey proteins enriched to a protein content of at most 4% by weight is heat-denatured to xe2x89xa680%, based on the proteins, by hot-holding at a temperature in the range from 75 to 150xc2x0 C. at a pH in the range from 5.0 to 7.0 under essentially non-shearing conditions, and that
b) a concentration step is then carried out, preferably to a concentration of the denatured whey proteins between 5 and 20%.
The expression used above, that the mean aggregate size (median) is between 1 and 4 xcexcm, means that, essentially, the aggregate size is to be between 0.1 and 10 xcexcm; in this case the median is defined such that at a given particle size distribution, 50% by volume of the particles are below this value and 50% by volume are above it. This median is also abbreviated in specialist circles to D50.3. If the aggregate size is to be xe2x80x9cessentiallyxe2x80x9d between 0.1 and 10 xcexcm, this is to be taken to mean the fact that more than 90% by volume, preferably more than 95% by volume, of the aggregates are in said particle size range between 0.1 to 10 xcexcm.
The inventive production process requires no shearing action, or only slight shearing action, so that complex apparatuses are not required.
An essential feature of the inventive process is that a controlled denaturation is carried out using the starting raw material in the inventively used temperature interval from 75 to 150xc2x0 C. by hot-holding at a pH in the range from 5.0 to 7.0 under essentially non-shearing conditions.
In particular, the degree of denaturation to be set according to the invention in the process procedure is xe2x89xa690%, preferably xe2x89xa695%. The control of the inventive process achieved by setting the degree of denaturation represents the significant difference between the inventive process and the processes known to those skilled in the art. This ensures that the yield of denatured whey protein aggregates is extremely high, so that virtually all of the protein present can contribute to achieving the desired properties.
If the heat denaturation is not carried out in a controlled manner, even very small variations in the composition of the starting materials, for example different contents of the protein fractions present in the starting solution, for instance milk or whey, in the pH of the starting solution and similar mean that the desired content of denatured (whey) protein aggregates is not achieved. As a result, the product obtained does not then have the desired properties and cannot be used for the intended purpose.
The content of denatured proteins is determined in the inventive process using the method described in the examples; this is a routine test as carried out in many laboratories in connection with other investigations. Details of the measurement of the degree of denaturation are therefore described in more detail in the examples below.
The degree of denaturation thus measured is a parameter which is simple to measure, which makes it possible for a person skilled in the art to achieve the object set using the inventive process.
In the inventive process, the starting material which can be used is any aqueous solution of whey proteins, for example whey, whey from casein manufacture. However, the raw material preferably used is a milk microfiltration permeate, or directly a non-enriched whey, in particular sweet whey. The protein content of the solution used does not exceed 4% by weight according to the invention, preferably not 3%. Therefore, according to the invention it is not necessary to produce a protein concentrate, for example a WPC (whey protein concentrate) before the inventive denaturation process is carried out. The inventively preferred raw material is, as indicated above, non-concentrated whey, preferably sweet whey, which has a denaturable whey protein content in the concentration range between 0.5 and about 1% by weight. In exceptional cases, the content of such a whey may be up to 1.2% by weight. The lactose content of such a whey is between 4 and 6% by weight.
According to the invention the pH of the starting material is 5 to 7, preferably between 5.5 and 6.5. Most preferred is a range of about 6, in particular 6.0 to 6.5. This offers the advantage that whey from cheese manufacture can be used in unchanged form. However, the raw material used can also be whey whose protein content has been increased by conventional dairy concentration processes to a maximum of 4% by weight, in particular a maximum of 3% by weight.
The hot-holding time to be employed at a defined temperature in the range specified above to achieve a whey protein denaturation greater than 80%, preferably greater than 95%, is between 18 hours and 10 seconds. Time limits which have a general validity may only be established with difficulty, since these can differ greatly from one another depending on the composition of the starting material (see DANNENBERG and KESSLER [xe2x80x9cReaction Kinetics of the Denaturation of Whey Proteins in Milkxe2x80x9d, J. Food Sci. 53(1), 258-263 (1988)], where the results of special studies of individual whey protein fractions are reported). However, the hot-holding time required when the inventive process is carried out results from the degree of denaturation to be maintained.
The inventive process can be carried out using conventional dairy apparatuses such as plate heat exchangers or tubular heat exchangers or vessels. During these processes, shear forces customarily occur due to pumping and stirring operations. However, according to the invention, and in contrast to the processes known to those skilled in the art, no further shearing operations are carried out, to the extent that the inventive process is carried out under essentially non-shearing conditions. The shear rates occurring due to the unavoidable pumping and stirring operations mentioned are generally not greater than 2000 sxe2x88x921 to 1000 sxe2x88x92, preferably not greater than 500 sxe2x88x921. The hot-holding of the raw material can also take place in complete absence of agitation.
According to the invention, the heat denaturation of the starting material, that is to say of the non-enriched whey, takes place in a temperature range between 75xc2x0 C. and 150xc2x0 C. However, particular preference is given to the temperature ranges between 110xc2x0 C. and 150xc2x0 C., and between 75xc2x0 C. and 95xc2x0 C., in particular 75xc2x0 C. After the inventive heat treatment the product is cloudy, but still liquid.
The whey proteins are present predominantly as aggregates. Measurement using a laser diffraction spectrometer (Coulter LS 130) gives a content of  greater than 90% by volume of the aggregates in the inventive size range from 0.1 xcexcto 10 xcexcm, and a content of  greater than 70% by volume in the preferred size range of 0.5 to 4 xcexcm (see FIG. 2).
The heating is followed according to the invention by a concentration using conventional dairy processes, preferably by ultrafiltration or microfiltration, to a protein content of 5% to 20%. After the concentration the product is viscous and has a creamy-smooth consistency. The aggregate diameter is not significantly changed by this step. It is a particular advantage of the virtually complete denaturation and aggregation of the whey proteins before the subsequent concentration step that removing non-denatured contents to increase the yield is not necessary.
The product thus produced can be used directly; alternatively, however, it can also be dried, preferably by freeze-drying or spray-drying.
The inventively produced product can be added to the cheesemaking milk for the manufacture of soft cheese, slicing cheese and hard cheese, in order to increase the whey protein content in these cheeses and the yield. In the denatured and aggregated form, the whey proteins remain in the cheese mass and are not lost in the whey, in contrast to native whey proteins, as is customary in classic cheese manufacture.
It is also possible to use the product in process cheese, in frozen and non-frozen desserts, in fresh cheese or in spreads. In all these products, by adding the inventively produced whey protein product, the fat content can be reduced, because of the creamy properties. In addition, the content of casein which is present, for example, in these products in the form of cheese raw material or skimmed milk powder, can partly be replaced, since denatured aggregated whey proteins behave in a similar manner to casein.
In a further very particularly preferred embodiment of the inventive process, the product obtained after carrying out the concentration is foamed with use of a foaming apparatus, with the pH being set to 4.0 to 5.5. When this process step is carried out, it is not necessary to add foam stabilizers. If foam stabilizers are added at all, which may possibly be desirable for further optimization of the foam structure, the amount of foam stabilizers used is considerably reduced, compared with conventional processes for producing foamed products. In the case of gelatin, for example, instead of the 0.5% to 1% gelatin customarily added, only about 0.1% is necessary.
The pH is set by controlled addition of an acid. The acid added is, according to the invention, an acid selected from the group of organic acids or acids approved for foods. Preference is given to a mixture of lactic acid and citric acid, in the most preferred case a mixture of 4 mol/l of citric acid and 90% strength lactic acid in equal parts.
After carrying out the foaming, a foamed essentially, or even completely, foam-stabilizer-free product is obtained. Compared with customarily foamed products, the inventive product is distinguished in that, in the foamed state, depending on storage conditions, it is physically stable in storage for weeks or even months. Customary products produced from whey protein aggregates achieve a storage like of this type, if at all, only by the addition of foam stabilizers.
The invention is described in more detail in all its embodiments by the examples given below.
In the figures:
FIG. 1 shows the relationship of the rate constants of denaturation of xcex2-lactoglobulin on pH, that is to say the change in the respective denaturation rate.
FIG. 2 shows by way of example the frequency distribution (content by volume versus particle diameter) of the whey protein aggregates produced by the inventive process. The accumulated content (% by volume) of the size classes which can be derived from the diagram is: